There is a general desire for sound transducers, such as loudspeakers, to provide high efficiency, high quality and increased sound levels with increasingly smaller dimensions. However, these preferences tend to be conflicting requirements resulting in a careful trade-off between different preferences.
For example, audio loudness is related to the amount of air that a loudspeaker displaces with the displacement being frequency dependant such that if the sound pressure level is kept constant then the lower the frequency, the bigger the required displacement. For these low frequencies the mechanical power handling of a loudspeaker is usually the limiting factor rather than the electrical power handling, and in order to provide the required sound levels relatively large physical dimensions tend to be needed. More specifically, sound reproduction with small transducers at low frequencies with a reasonable efficiency and sound level is very difficult as the efficiency is inversely proportional to the moving mass and proportional to the square of the product cone area and force factor.
In order to obtain high sound levels and efficiency from small and typically cheaper devices, transducers can be used which have a high resonance peak (high Q value). However, this tends to result in reduced audio quality and in particular tends to provide a low frequency (bass) sound which is often perceived as booming with a relatively high bass sustain or ringing.
European Patent Application EPO4769892.3 discloses a system wherein a given sound pressure level can be achieved by a sound transducer with reduced physical dimensions. In accordance with the proposed system, a low frequency band of a signal is replaced by a fixed single frequency carrier signal with a frequency close to a resonance frequency of a loudspeaker. The amplitude of the carrier follows the amplitude of the signal components falling in the low frequency band. Thus, effectively a low frequency signal component is replaced by a single tone carrier with an amplitude equal to the signal component. Thus, by concentrating the low frequency signal into a single carrier frequency close to the resonance frequency of the loudspeaker, a much higher efficiency of the loudspeaker can be achieved. Furthermore, as the mechanical power handling and air displacement capability of a loudspeaker is highest around the resonance frequency, smaller dimensions of the sound transducer can be achieved by this approach.
However, although the approach can provide substantial advantages in many scenarios it also has some associated disadvantages. In particular, the approach tends to distort the low frequency sound signal and may in some scenarios result in a suboptimal sound quality.
Specifically, in some scenarios and environments, some listeners have indicated that the generated sound sometimes may be perceived more boomy or tonal than preferred. In particular, in some scenarios a very high Q-factor of the transducer may result in the generated signal being perceived to continue to ring longer than the original signal.
Hence, an improved audio system would be advantageous and in particular a system allowing increased flexibility, facilitated implementation, improved audio quality, increased efficiency, reduced physical dimensions of a sound transducer and/or improved performance would be advantageous.